In recent years, as one type of radio communication system, WiMax (Worldwide Interoperability for Microwave Access) systems have gained increasing popularity.
FIG. 1 is a schematic diagram showing an exemplary structure of an ordinary WiMAX system.
The ordinary WiMAX system shown in FIG. 1 is provided with MS 1000, NAP 2000, and NSP 3000.
MS 1000 is a mobile communication terminal (MS: Mobile Station) that performs radio communication. Alternatively, MS 1000 may be a service station (SS: Service Station) that is an ordinary terminal that subscribes to a service.
NAP 2000 is a network access provider that is a provider that provides an access line through which MS 1000 is connected to a network.
In addition, NAP 2000 is provided with ASN 2100 that is an access service network (ASN: Access Service Network). Moreover, ASN 2100 is provided with ASN-GW (ASN-GW: Access Service Network—Gate way) 2200 that is a connection gate way that connects ASN 2100 and CSN 3100 (that will be described later) through R 3 (Reference Point 3).
NSP 3000 is a network service provider (Network Service Provider) that is a provider that provides MS 1000 for a service.
In addition, NSP 3000 is provided with CSN 3100 that is a core service network (CSN: Core Service Network). Moreover, CSN 3100 is provided with AAA 4000 and a plurality of HA 5000-1 through 5000-6.
AAA 4000 (AAA: Authentication, Authorization, and Accounting) is an authentication server that authenticates a user when he or she tries to connect MS 1000 to a network.
HA 5000-1 through 5000-6 (HA: Home Agent) are connection devices that connect MS 1000 and the network. It should be noted that although FIG. 1 shows 6 HAs, the number of HAs is not limited thereto.
In the system structured in such a manner, when MS 1000 is connected to the network, AAA 4000 dynamically assigns an HA that connects MS 1000 and the network from HA 5000-1 through 5000-6 (for example, refer to Non-Patent Literature 1).
In the following, a communication method employed for the WiMAX system structured as shown in FIG. 1 will be described.
FIG. 2 is a sequence chart describing an exemplary communication method employed for the WiMAX system structured as shown in FIG. 1.
When MS 1000 is connected to the network, the device/user of MS 1000 is authenticated.
At step 61, an EAP RQ Identity that requests identification information (Identity) based on an extensible authentication protocol (EAP: Extensible Authentication Protocol) is transmitted from ASN-GW 2200 to MS 1000.
Then, at step 62, an EAP RP Identify that is a response (RP: Response) to the EAP RQ Identity is transmitted from MS 1000 to AAA 4000.
Thereafter, at step 63, an authentication processing sequence is performed between MS 1000 and AAA 4000. When AAA 4000 successfully authenticates MS 1000, then at step 64, an EAP Success that denotes that the authentication is successful is transmitted from AAA 4000 to NAP 2000. In the authentication processing sequence at step 63, an HA address with respect to each MS 1000 is issued (assigned) to ASN-GW 2200 by AAA 4000. Such a specific issuance method has not yet been established. Here, the case in which HA 5000-1 has been assigned is exemplified and it will be described below.
When the EAP Success is received by ASN-GW 2000, then at step 65, the EAP Success is transmitted from ASN-GW 2200 to MS 1000.
Thereafter, the connection for MS 1000 is authenticated.
At step 66, a DHCP (Dynamic Host Configuration Protocol) Discover that is a signal that serves to obtain an IP (Internet Protocol) address is transmitted from MS 1000 to ASN-GW 2200.
Then, at step 67, a Registration Request that is a signal that serves to request registration is transmitted from ASN-GW 2200 to HA 5000-1.
When the Registration Request is received by HA5000-1, then at step 68, an Access Request that is an access request signal that serves to request access is transmitted from HA 5000-1 to AAA 4000.
When the connection for MS 1000 is successfully authenticated by AAA 4000, then at step 69, an Access Accept that is a signal that serves to permit access is transmitted from AAA 4000 to HA 5000-1.
When the Access Accept is received by HA 5000-1, then at step 70, a Registration Reply that is a reply signal to the Registration Request is transmitted from HA 5000-1 to ASN-GW 2000.
Then, at step 71, a DHCP Offer in which an IP address that can be assigned to MS 1000 is embedded as “a user IP” is transmitted from ASN-GW 2200 to MS 1000.
Thereafter, a charging process is performed between HA 5000-1 and AAA 4000.
At step 72, an Accounting Request that is a charging information notification signal that is notified of charging information is transmitted from HA 5000-1 to AAA 4000.
Then, at step 73, an Accounting Response that is a response signal to the Accounting Request transmitted from HA 5000-1 at step 72 is transmitted from AAA 4000 to HA 5000-1.
At steps 74 and 75, the above-described Accounting Request and Accounting Response are exchanged between HA 5000-1 and AAA 4000 at a predetermined cycle and are based on a predetermined trigger.
Thereafter, at step 76, a signal (DHCP Release) that serves to return the IP address from MS 1000 is transmitted to ASN-GW 2200, and then, at step 77, a Registration Request in which “Lifetime” that represents the expiration of registration is set to “0” is transmitted from ASN-GW 2200 to HA 5000-1.
When the Registration Request is received by HA 5000-1, then at step 78, a Registration Reply that is a reply signal to the Registration Request is transmitted from HA 5000-1 to ASN-GW 2000.
Then, at step 79, the Accounting Request is transmitted from HA 5000-1 to AAA 4000. The Accounting Request that is transmitted contains information that denotes that the charging process is going to be completed.
Then, at step 80, the Accounting Response that is the reply signal to the Accounting Request transmitted from HA 5000-1 at step 79 is transmitted from AAA 4000 to HA 5000-1.
FIG. 3 is a sequence chart that describes another exemplary communication method employed for the WiMAX system structured as shown in FIG. 1. Here, the case in which HA 5000-2 has been assigned by AAA 4000 is exemplified and it will be described below. In this example, the case in which the existing load state of HA 5000-2 is “congestive” where HA 5000-2 cannot further perform the process will be described.
Like the connection method described with reference to FIG. 2, when MS 1000 is connected to a network, the device/user for MS 1000 is authenticated.
At step 91, an EAP RQ Identity that requests identification information based on the extensible authentication protocol is transmitted from ASN-GW 2200 to MS 1000.
Then, at step 92, an EAP RP Identify that is a response to the EAP RQ Identify is transmitted from MS 1000 to AAA 4000.
Thereafter, at step 93, an authentication processing sequence is performed between MS 1000 and AAA 4000. When AAA 4000 successfully authenticates MS 1000, then at step 94, an EAP Success that denotes that the authentication is successful is transmitted from AAA 4000 to ASN-GW 2000. In the authentication processing sequence at step 93, an HA address with respect to each MS 1000 is issued (assigned) to ASN-GW 2200. In this case, the address of HA 5000-2 is issued.
When ASN-GW 2000 receives the EAP Success, then at step 95, the EAP Success is transmitted from ASN-GW 2200 to MS 1000.
Thereafter, the connection for MS 1000 is authenticated.
At step 96, a DHCP Discover that is a signal that serves to obtain an IP address is transmitted from MS 1000 to ASN-GW 2200.
Then, at step 97, a Registration Request that is a signal that serves to request registration is transmitted from ASN-GW 2200 to HA 5000-2.
Then, since HA 5000-2 is “congestive,” at step 98, the Registration Request transmitted from ASN-GW 2200 is discarded by HA 5000-2.
Thus, MS 1000 enters a disconnectable state.
In such a manner, although AAA 4000 assigns HA 5000-1 through 5000-6 to connect MS 1000 to the network, the assignment method is not yet established. As a result, depending on the operation (load) states of HA 5000-1 through 5000-6 assigned by AAA 4000, it may not be possible for MS 1000 and the network to be connected. To avoid such a situation, when AAA 4000 assigns one of HA 5000-1 through 5000-6, it is necessary to assign it in such a manner that the load states of HA 5000-1 through 5000-6 are distributed.
Thus, a load distribution device that distributes the processes performed by a plurality of processing devices (SIP servers) such that the processes are not concentrated in one part of each processing device has been contemplated (for example, refer to Patent Literature 1).
In addition, an AAA server that selects one home agent from among a plurality of home agents held in a management table based on a predetermined load distribution algorithm upon connection of a mobile terminal equivalent to MS 1000 to the network has been disclosed (for example, refer to as Patent Literature 2).